Antenna and lobe switcher



Nov. 15, 1949 N. E. LINDENBLAD 2,488,419

I ANTENNA AND LDBE SWITCHER Filed June so, 1943 s Sheet-Sheet 1 H: mm

XNVENTOR M45 5. A/NDE/VBLAD.

ATTORN EY Nov. 15, 1949 N. E. LINDENBLAD 2,488,419

ANTENNA AND LUBE SWITCHER Filed June 30, 1 943 6 Sheets-Sheet 2 INVENTOR /V/L5 E. L/NDENBLAD- ATTOR N EY Nov. 15, 1949 N. E. LINDENBLAD ANTENNA AND LUBE SWITCHER 6 Sheets-Sheet 3 Filed June 30, 1943 INVENTOR A045 .5 imam/5440.

Y B ATTORNEY Nov. 15, 1949 Y N. E. LINDENBLAD ANTENNA AND LOBE SWITCHER 6 Sheets-Sheet 4 Filed June 30, 1945 1U INVENTOR /V/45 E lm/m-waz/m Nov. 15, 1949 N. E. LINDENBLAD 2,488,419

ANTENNA AND LOBE SWITCHER Filed June 50, 1943 6 Sheeis-Sheet 5 ATTO R N EY Nov. 15, 1949 N. E. Ll N-DENBLAD ANTENNA AND LOBE SWITCHER 6 Sheets-Sheet 6 Filed June 30, 1943 EU 3 w? wwx R a M RB Y 3 M T 5 v QT N T 1 A 5 SY MB Patented Nov. 15, 1949 to Radio Corporation of of Delaware America, a corporation Application June 30, 1943, Serial N0. 492,805

32 Claims. I

The present invention relates to antenna sys terns and, more particularly, to sharply directive antenna arrays for radio locator use and to the associated transmission line system for connecting said arrays to the accompanying transmitter and receiver equipment.

In obstacle detection systems, which are sometimes known as radio locator systems, it has been proposed to cause a small deflection of a radio beam at regular intervals through the four quadrants of a circle which is perpendicularly located to the mean axis of the beam. This operation, commonly known as lobe switching, may be done in many ways. For example, if. a broadside antenna array is used the deflection may be accompli'shed by causing small variations in the phase distribution of energy in the array. This methodlends itself inherently to-remote lobe switching, that is, a causation of the deflection from a point at some distance from the antenna structure itself. Another way which may be used in conjunction with a parabolic reflector involves moving the antenna element itself about the focus. This operation may be done with or without changing the plane of polarization. If the plane of polarization is changed" the plane may be alternately vertical and horizontal. Basically, the moving antenna element type of lobe switching is less readily adaptable to remote operation. It is, however, under some conditions, more desirable since the parabolic reflector array has a more natural tendency toward freedom from secondary lobes or ears in the antenna pattern.

In accordance with the principles of the present invention. it is proposedto overcome the disadyantages of this last mentioned system of lobe switching by utilizing a fixed parabolic reflector with a radiating element associated therewith positioned at about the focus of the parabolic reflector. The radiating element is adapted to be unsymmetrically energized in such a manner that an unsymmetrical beam is radiated. The unsymmetrical energizing can here be of the amplitude type since a change in location of the focal system translates into changed phase distribution along the surface of the parabola. A plurality of transmission lines, one for each proposed mode of un" symmetrical energization are arranged to be successively connected to the associated transmitter in such a way thatv the resultant radio beam is regularly deflected through the four quadrants of the circle perpendicular to the mean axis of the beam.

In applying the principles of the present invention a parabolic reflector of a foraminous or open. mesh metallic construction may be used if desired so that the antenna may be placed over the face of a searchlight, for example, and project a radio beam having a mean axis aligned with the line of light from the searchlight. Due to the open mesh metallic construction of the reflector and the comparatively small size of the remainder of the elements of the antenna very little light is cut off from the searchlight beam.

The antenna, as thus described, may be used as a transmitter for transmitting radio wave impulses of extremely short duration. Due to the high directivity of the antenna system pulses are returned from objects lying within a narrow range of angles with respect to the mean axis of the radio beam and, also,.of course, of the searchlight. The transmitter itself may be generally of the type described in my prior application, Serial #'441,311, filed May 1, 1942, now Patent No. 2,411,140, issued November 12, 1946. In this transmitter an. oscillator is excited periodically through a spark gap which is connected in series between the oscillator and a charging voltage source and to which is supplied at periodic intervals a voltage of sufiicient value to break down the gap. An application copending with the above identified application and filed by C. W. Hansell, Serial #427,266, filed January 19, 1942. now Patent No.. 2,455,673, issued December 7, 1943, also describes generally the principles of the radio locating system to which the present invention may be applied.

The radiating element of the antenna of the present invention which, as before stated, is unsymmetrically energized preferably has the mode of energization switched by a motor so that a pulse of high frequency energy is radiated in regular succession in each of the four quadrants of the reflector. If, for example, the motor rotates at a speed of 60 revolutions per second the pulses may be radiated- 240 times per second corresponding to a pulse for each quadrantal position of the beam for each revolution of the antenna switching structure. The up and down beam firing positions determine the vertical position of the object to be detected, while the right and left beam firing positions determine the horizontal positions. The radiating patterns or lobes of the beam will, of course, be diiierent for difierent quadrants of the circle as the switching means is rotated. However, the antenna systern is so designed that the main lobes of the radiation patterns overlap in the up and down beam firing positions and, also, in the right and left beam firing positions, The reflected pulses which I are received are viewed on a pair of cathode ray Oscilloscopes, one of which indicates the pulses received during the up and down beam positions and the other of which indicates the pulses received during the right and left beam positions. The impulses shown on each oscilloscope may thus easily be compared in amplitude. Since the time interval between radiated impulses is quite long compared to the time of each pulse it will be understood that a pulse reflected by a remote object to be detected will be received at the associated receiver during the same quadrant of revolution in which the original pulse was radiated. If pulses which are reflected from a remote object are radiated, for example, in the up and down positions of the revolving radiating element the reflected pulses will be received during the same positions. If these received impulses are of equal intensity it therefore follows that the vertical plane of the antenna system is pointed at the object. Likewise, if the reflected positions received during the right and left positions of the directivity pattern are also of equal intensity it follows that the horizontal plane of the antenna system is also pointed at the object. Under these conditions, the object is directly on the mean axis of the radiation patterns of the antenna system. Since the axis of the parabolic reflector of the antenna is coincident with the light beam from the Searchlight with which it may be associated, the searchlight will illuminate the object when turned on after locating the target. If the received pulses reflected from the object are of unequal intensity it is an indication that the antenna and the Searchlight are not pointing directly at the object but to one side thereof. The operator viewing the oscilloscopes may then make appropriate corrections in the orientation of the antenna and Searchlight structure.

In the foregoing description it has been assumed, for convenience in description, that the system is so arranged that the mean axis of the beam is more or less horizontal. In actual practice, of course, the axis may be directed upwardly at angles nearly vertical so that there are in reality no actual up and down positions of the radiator. The operation, however, is the same.

As has been pointed out above, it is desirable that the switching of the lobes of the directivity pattern of the antenna be accomplished from a remote location.

An object, therefore, of the present invention is to provide an antenna system utilizing a parabolic reflector wherein the lobe switching may be remotely accomplished.

Another object of the present invention is the provision of an antenna system for producing a sharply directive radio beam which is readily deflected through four quadrants of a circle perpendicular to the mean axis of the beam.

Another object of the present invention is the provision of an antenna having a steerable directivity pattern.

Still another object of the present invention is the provision of a novel means for energizing a directive antenna structure from a source of high frequency energy.

A further object of the present invention is the provision of an antenna system for radio locators.

Still a further object of the present invention is the provision of an antenna system, as aforesaid, in which the alternate lobes may have either alternating polarization or the same polarization, as desired.

Still a further object of the present invention is the provision of a system, as aforesaid, in which the receiving antenna structure, while physically a part of the transmitting antenna structure, is electrically so rotated therefrom that it need not be switched.

The foregoing objects, and others which may appear from the following detailed description, are attained in accordance with the principles of the present invention by providing a radiating element in the form of a plane conductive sheet or table which is arranged to be unsymmetrically energized in a plurality of different modes in regular succession. The radiating element may be located at the focus of a parabolic reflector and at a desired remote location a lobe switching system is arranged for accomplishing the successive modes of energization of the radiating element. Furthermore, means may be provided for switching the antenna and transmission line system from a condition for transmitting energy to a condition for receiving energy reflected from the object to be detected.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates schematically the arrangement and inter-connection of antenna, switch, transmitter and receiver as used in the present invention, while Figures 2 and 3 show in plan and elevation, and in more detail, the construction of the radiating element which may be associated with the reflector system of Figure 1; Figure 4 illustrates in more detail, and in partial cross-section, the details of construction of the lobe switching arrangement, while Figure 5 illustrates a modification of the energizing means for the radiating element and a different type of lobe switcher, while Figures 6 and '7 show in elevation and in plan, also partly in section, a preferred arrangement of the modification of Figure 5, and Figures 8 and 9 show in elevation and plan a further modification of the present invention, while Figure 10 illustrates, in section, still a further modification of the invention.

Referring, now, to Figure 1, there is shown a parabolic reflector II which may be, as pointed out above, of foraminous or open mesh construction, in order that it may be conveniently mounted over the face of a searchlight. At the focus of the reflector II is located a radiating element l3 which is arranged to be successively energized from transmission lines l5, [7, I9 and 2c, in four unsymmetrical modes, in order to produce a warped directivity pattern which is rotated through the four quadrants of the circle normal to the axis of the reflector H. The successive energization of transmission lines l5, ll, it and 2B is accomplished by a rotary switching arrangement 22 driven by motor 23. From the switching arrangement 22, transmission line 24 passes to a further switching arrangement 25 by means of which transmitter 26 and receiver 27 are alternately and selectively connected to transmission line 24. The switching arrangement 25 is commonly known as a TR box and the details of one form of such a TR box is shown in my prior application, Serial #477,435, filed Feb. 27, 1943. It is sufficient for the present purpose to merely state that the switching arrangement 25 involves no moving parts but only a plurality of resonant circuits so associated with spark gaps or other electrical discontinuities that when the transmitter is energized the spark gaps or electrical dis- *"ceiver 22". by transmitter 26 ceases, the electrical discontiaccents continuities breakdown to so connect the resonant circuits as to present a low impedance for energy'proceeding from the transmitter '26 to the transmission line 24 and an extremely high impedance for energy from transmitter 2a to re- When the pulse of energy generated nu'iti'es are restored and the transmission line from transmitter 26 then presents a high impedan'ce to energy from transmission line 24, while the transmission line from receiver 2? presents a low impedance to energy from transmission line 2'4. Thus energy is transferred from transmission line 24 to receiver 27 with very little being dissipated in the transmitter 25.

The radiating element of Figure 1 is shown in more detail in Figures 2 and 3.

As may be'seen from Figure 2 the radiating element consists of a conductive rectangular conductive plane or plateau 35 surrounded on all sides by a conductive walled indentation or moat 32. This indentation has a depth of a quarter wavelength and thus causes the surface to be efiectively isolated .from the surrounding surface '33 at the operating frequency of the system. At the midpoints of each of the sides of the conductive plateau 5d are connected the inner conductors 35, 31, 39 and 55 of transmission lines l5, l7, l9 and ill. When the antenna of Figures 2 and '3 is energized at One point at a time as, for example, at the point of connection of inner conductor 35, the antenna exhibits an unbalance in its radiation pattern, that is, the main lobe of the directivity pattern will be found to incline somewhat toward the side to which the energizing potentials are applied. That is, in viewing Figure 2,'the .zn'ain lobe of the directivity pattern will extend upwardly from the plane of the drawing but slightly toward the left. If the radiator 25 is energized from conductor 3.? the main lobe will be inclined slightly toward the top of the sheet. If conductors 3'5 or 43 are energized, the main lobe will be correspondingly deflected. This characteristic of surface current or slot antennas has been mentioned in my prior appication, Serial No. 448,743, filed June 27, 1942, now Patent No. 2,414,266 granted January 14, I947.

The antenna of Figure 2 may be considered as a surface current antenna which may be equally F fed for planes of polarization perpendicular with respect to each other. Now, if the antenna is fed successively through the four transmission lines (5., ll, l9 and 25 the main lobe formed and reflected by the parabolic reflector ll of Figure 1 7 describes a rotation of deviation. The alternate lobes from the antenna energized as described have alternate planes of polarization. This lat- 'ter feature is not, however, a requisite of the invention but an expedient in design.

-The switching device 22 selecting one of the transmission lines 55, ll, l9 and 25, over which a pulse is transmitted, is shown in more detail in Figure 4 and its operation is based on the principle of shifting of location of nodal points on" unloaded transmission line elements by quarter wave extensions. This shifting is performed by a motor driven rotary element. The lobe switcher 22 consists of four trap circuits 45, 31, t9 and 50, of which only trap circuits 45 and id are visible in Figure 4, and only $9 is shown in section to show the interiorconstruction. Each trap circuit consists of one wavelength section of concentric transmission line having an outer casing line section is short-cl-rcuited at each end by conductive plates 53 and 54! closing the ends of the outer shell 5|. At point 55 spaced from the top end of trap circuit 49, a distance equal to one quarter of the operating wavelength, is connected the inner conductor 38 of transmission line is leading to the antenna system. In a similar way transmission lines l5, ll and 25 are connected to trap circuits 45, t? and 59. At each of the points 55 is also connected a connection to the end of shell 34 of transmission line 24. This shell is surrounded by an outer casing it for a distance equal to one quarter of the operating wavelength. The casing is connected to shell 34 at one end and closed at the other. The inner conductor as of transmission line 24, witlicasing 46, extends beyond shell as a distance equal to a quarter wavelength, the exact length being readily adjustable by means of the slidable outer sleeve -44 At point 56, a distance equal to one quarter of the operating wavelength from the other end of conductor 52 of each of the trap circuits 45, 51, 49, 5B is connected a plate 51 extending radially inwardly of the system a distance equal to one quarter of the operating wavelength. The four inwardly extending plates are contained within a housing 58. The rotating shaft of motor 23 extends axially through the center of housing 58 and carries a rotor including a pair of parallel plates 59, each having a length equal to one quarter of the operating wavelength and also including an axial extension 60, likewise having a length equal to a quarter wavelength. A quarter wave'trap El is provided between the end of the rotor adjacent the motor and the motor shaft itself to electrically free that end. Now when one of the plates 5! is covered by the parallel rotary plates 59, its electrical characteristics become equivalent to a quarter wave extension and trap 49 lets power pass by point '55 along conductor 39. That is, plate 51 when covered by rotary plates 59 presents a high impedance to energy of the operating frequency at point 56. Due to the half wavelength spacing between points 5&3 and 55 along conductor '52 a high impedance to the operating energy is also presented at point 55. The quarter wave distance between point 55 and the end of shell 34 causes a low impedance to energy of the operating frequency to be presented at the junction of conductor 39 and shell 34. Thus energy is transmitted through transmission line I9 to the antenna. When parallel rotary plates 59 uncover plate 51 point 56 becomes of extremely low impedance to the operating frequency and similarly point 55 becomes low impedance. This causes a high impedance to be presented at the junction of line 39 and shell 3 t so that no energy flows along line 39. Since the current required to feed the rotary plate at the free high impedance end of the plates is very low, the internal current in the combined plate system is very low. Consequently, the voltages in each trap circuit of the system are also low. However, in order to prevent spurious sparking at unexpected times between the plates when using restricted spacings it has been found desirable to aid the sparking to become continuous rather than to attempt to counteract it. Spark gaps 62 have therefore been provided between plates 55 and 55. The motor 23 which drives the lobe switcher may, if desired, be arranged to drive a pulse instigator energizing transmitter 26 so that the two will always 'be synchronous and firmly "5'1 'an'd'aninner conductor '52. 'The'transmission '75 cover a constant angular band.

If it is desired to radiate energy having only one polarization the antenna feed may be arranged as shown in Figure 5. Furthermore, this modification provides for switching of only the transmitted energy, the received energy not being transmitted over the rotary selector. If this is done the echo is received by the antenna in a state of an undefiected single main lobe. This may be desirable in order to reduce lobe wobble which, of course, shows up as a product of transmitted and received eifects. In this modification, the radiating plateau 30 is arranged to be fed for one quadrant in a push-pull relationship at points It and II through transmission lines I2 and I5. These lines are connected to a conversion circuit I4 for converting from push-pull to the single ended line H. The converting circuit includes an outer shell I5 surrounding the shell I6 of transmission line ii for a distance equal to a quarter of the operating wavelength and connected to the outer shell at its end. Thus the extreme end of shell 76 is electrically freed from the remainder of the shell of the transmission line and is permitted to assume a polarity instantaneously equal and opposite to that of the inner conductor of the transmission line TI. The theory of operation of such a conversion circuit for coupling between single-ended or unbalanced pushpull lines is more fully described in my prior Patent #2,238,904, granted April 22, 1941, to which reference may be had for a more complete description. It is enough for the present purposes to understand that the unbalanced line H is by this means enabled to apply energy in a push-pull relationship to points Ill and II on the radiating sheet or plateau 35. Since points I0 and H are located above the center of the radiating sheet 35, the resultant radiating lobe will be directed upwardly from the plane of the sheet of the drawing and slightly toward the top of the figure. For a radiating lobe inclined in the opposite direction, that is, toward the bottom of the figure, the radiating plateau 30 is fed in a pushpull relationship at points 88 and SI near the lower edge of sheet 30. This energization is performed through transmission lines 82 and 83 obtaining push-pull energy from transmission line 81 by means of a conversion circuit 85 similar to conversion circuit M, described above. To obtain a radiating lobe inclined in the direction toward the left of the figure, the radiating plateau 30 is energized at point 95 through transmission line 92 and for the remaining quadrant the plateau is energized at point 9| through transmission line 93. Since points 90 and EH are near the electrical center of the right and left hand edges of the radiating sheet 35, the energization will be unsymmetrical because of the fact that only one edge at a time is energized. The successive energization for the four quadrants is performed by rotary selector I52 which operates very much in the same way as the distributor of a four cylinder automobile. The rotary brush I53 of selector I52 successively sweeps by contacts connected to the inner conductors of each of the transmission lines TI, 87, 52 and 93. When a pulse of energy is applied to transmitter 25 the resultant radio frequency energy is conducted along transmission line I24 to brush I53 and the energy will spark across to the one of the inner conductors which is nearest at the time.

In order to obtain a single undefiected main lobe for reception of the reflected energy, receiver 21' is connected by means of transmission line I21 to a conversion circuit I28 similar to conversion networks I4 and 84. Thus conductors I04 and I05 passing across slot 32 at substantially the midpoints of each side of the radiating sheet 30 receive energy in a push-pull relationship from the edges of the sheet. This is converted to unbalanced energy in the conversion circuit I28 for transmission along the coaxial transmission line IZ'I to receiver 21. In order to prevent energy from the transmitter 26 from affecting receiver 21 conductors I04 and I05 extend across the slot 32 into quarter wave trap circuits I25, I26 and are terminated therewithin by electrical discontinuities or spark gaps I56, I01. Thus, when the transmitter is in operation the energy picked up by conductors I04, I05 causes these electrical discontinuities to break down and effectively shortcircuit the receiver transmission line.

It will be apparent, that in this modification of the invention no tuned lobe switches are necessary and the received signal does not at any time enter the switching system.

Figures 6 and '7 show in somewhat more detail a modified physical embodiment of the structure shown in Figure 5. The same reference characters have been applied to these figures as appear in Figure 5. Thus radiating sheet 30 is surrounded by an isolating groove or trench 32 operating in the same way as the element identified by the same reference character in Figure 5. When the sheet or plateau 30 is energized by energy appearing on conductors I0 and II, a lobe leaning in one direction results while energization of conductors and 8| results in an oppositely leaning lobe. Similarly alternate energization of conductors I04 and I55 alternately produces a lobe of energy in the remaining quadrants. Conductors and Eli, as before, go to the receiver equipment. The unbalanced to balanced line converter of Figure 6 has an additional quarter wave stub IS in an end-to-end relationship with inner sleeve I6. This additional stub acts to improve the electrical balance on conductors I0 and 'II. However, the electrical operation is essentially the same.

Figure 8 shows a further modification of the lobe switching structure which may be used instead of the lobe switcher 22 of Figure 1. In this form of construction the transmission line 24 from the TR box is divided into four separate branches, two of which, I50 and I5I, are shown. These branches are all one quarter of the operating wavelength long and each terminate within a separate resonant line section, such as chambers I55 and I5! of Figure 8. The resonant line sections I55, I55, I57 and I58 each consist of a quarter wavelength outer shell I59 and an equal length inner conductor I88, mounted on and connected together at one end by plate NH. The quarter wave branches I58 and I5I are connected to the inner surface of shell I59 of the appropriate line sections I55 and I57 at such distance from the lower closed ends thereof as to assure an appropriate impedance match between the transmission line and the interior of the line section. Similarly, each of the transmission lines from the antenna system I5, I'I, I9 and 2!! pass through the lower end of line sections I55 to I58 and are connected to the inner wall of outer casing I59 at a distance from the closed end such that an impedance match is attained between the impedance of the transmission lines and the tuned line section. Each of the tuned line sections I55 to I58 are open at the end remote from plate I6I and over their open ends is arranged a shutter disc I63 having therein a single aperture I64 adapted to: successively pass over the open ends of each of the line sections I55 to I58. The shutter disc is rotated by means of motor 23.. Now when the aperture I64- is over one open end, for example, that of line section [55, it becomes in effect a quarter wave line section short-circuited at one end and open at the other. Thus resonance is attained and energy is transmitted from transmission line I50 to transmission line I and energy is radiated from antenna ll of Figure l in one lobe. No energy is applied to. any of the other transmission lines 11, I9 and 20 because the shutter disc being imperforated over the corresponding line sections I56, 451 and I58 so detunes them that substantially no coupling exists between transmission line 24 and transmission lines I1, l9 and 28..

The system shown in Figure is similar in principle of operation to that shown in Figures 8 and 9 but is so arranged as to avoid the use of transmission lines between the lobe switching structure and the radiating elements. The assembly shown in Figure 10 therefore, adapted to be placed in its entirety at the focal point of the parabolic reflector of Figure 1 and so arranged that the motor 23 is directed away from the refiector I I. This modification includes four radiator elements, one for each quadrant of the radiated beam. Only two opposing radiators 2M and 2&2 are shown. Each radiator is provided with sl-idable extension sleeves 2G4 and 296 for tuning the radiator. Each radiator is supported in place by an insulated support bracket. 299 from the main supporting plate 21a. The radiating elements are radially arranged about a common center point and their inner ends are terminated by downwardly turned portions 2 which face axially arranged quarter wave rods 2M to 2H5. These quarter wave rods are enclosed within a conductive walled chamber 223. Between the ends of the down-turned ends 2| l of the radiator elements and the free ends of rods 2M to 215, is provided a shutter disc 223 having a single aperture 224 therein adapted to be successively aligned with each of the rods zl t to ZIB. When, for example, the aperture 224 appears between rod 2M. and the associated radiator 288, energy supplied to rod .ZIA from the transmitter is coupled to the radiating element 258. All of the other radiating elements are uncoupled from the transmitter, not only due to the fact that there is no aperture permitting coupling from down-turned ends 2 I l and the associated rod, such as rod 2l6, but, also, because of the detuning eiiect on rod 2H3 by the presence of the shutter disc 223 adjacent the end of the rod. The coupling and uncoupling of the transmitter to the successive radiator elements of Figure 10 is very similar in its theory of operation to that described with respect to the structure shown in Figures 8 and 9. Figure 10, however, diliers somewhat in the manher of exciting the rods 2M to 2l6 within the casing 220.

In the modification of this figure, the transmission line 2d enters the casing 22% through a quarter wave sleeve 225 thus permitting the interior end of the outer casing of transmission line 22 3 to be electrically freed from the casing. The inner conductor 44 of transmission line 2 3 is connected to such a point along sleeve 22B surrounding the shaft from motor 23 that an impedance match is attained between the impedance of transmission line 24 and the impedance of sleeve 226. The sleeve 226 at the end remote from motor 23 is flared out into a fiat conductive 10 plate; 22? having apertures therein through which the resonant rods 2M. to 2l6 pass. Thus the energy carried by sleeve 226 is coupled to the resonant rods 2M to- H6.

While I have illustrated a particular embodiment of the presentinvention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement and it is, therefore,v contemplated by the appended claims to cover any such modifications as fall within the spirit and scope of the invention.

I claim:

1. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated, at the operating frequency, from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, and means for selectively energizing said sheet in a plurality of different modes.

2. In an antenna system, a radiator including a. plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at. the operat ng frequency, from surrounding structure along its entire periphery and means for selectively energizing said sheet in a plurality of different modes to provide in succession a plurality of highly directive beams of energy, each having their maxima deflected from a line normal to the plane of said sheet.

3. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated, at the operating frequency, from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, and means for selectively energizing said sheet in a plurality of difierent modes to provide in succession a plurality of highly directive beams of energy, each having their maxima deflected from a line normal to the plane of said sheet.

4. In an antenna system, a radiator including a plane rectangular conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated, at the operating frequency, from surrounding structure along its entire periphery and means for selectively energizing said sheet in a plurality of different modes, said means including a plurality of transmission lines, each having a conductor coupled to one side of said sheet and means for selectively connecting said transmission lines to a source of high frequency energy.

5. In an antenna system, a radiator including a plane rectangular conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery and means for selectively energizing said sheet in a plurality of difierent modes, said means including a plurality of transmission lines, each having a conductor coupled to substantially the midpoint of one side of said sheet and means for selectively connecting said transmission lines to a source of high frequency energy.

6. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half Wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel hav ing conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of transmission lines each having a conductor passing across said channel and connected to one side of said sheet, and another conductor connected to the outer side of said channel, and means for selectively connecting said transmission lines to high frequency transducer equipment.

7. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated, at the operating frequency, from surrounding structure along its entire periphery by a channel havin conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of transmission lines each having a conductor passing across said channel and connected to substantially the midpoint of one side of said sheet, and another conductor connected to the outer side of said channel, and means for selectively connecting said transmission lines to high frequency transducer equipment.

8. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of coaxial transmission lines each having an inner conductor passing across said channel and connected to one side of said sheet, and an outer shell connected to the outer side of said channel, and means for selectively connecting said transmission lines to high frequency transducer equipment. 7

9. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive Walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of coaxial transmission lines each having an inner conductor passing across said channel and connected to substantially the midpoint of one side of said sheet, and an outer shell connected to the outer side of said channel and means for selectively connecting said transmissi-on lines to high frequency transducer equipment.

10. In a radiant energy system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding struc-l ture along its entire periphery by a channel hav-' ing conductive walls and passing around said periphery, the depth of said channel beingof the order of one quarter of the operating wave length, a plurality of transmission lines each having a conductor passing across said channel 12 and connected to one side of said Sheet, and another conductor connected to the outer sid of said channel, and means for selectively connecting a transmitter and a receiver to each of said lines in regular succession.

11. In a radiant energy system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of transmission lines each having a conductor passing across said channel and connected to substantially the midpoint of one side of said sheet, and another conductor connected to the outer side of said channel, and means for selectively connecting a transmitter and a receiver to each of said lines in regular succession.

12. In a radiant energy system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery and means for selectively energizing said sheet in a plurality of different modes to provide in succession a plurality of highly directive beams of energy, each having their maxima deflected from a line normal to the plane of said sheet, and further means for so coupling a receiver to said radiator that the maximum response of said system is along a line normal to the plane of said sheet.

13. In a radiant energy system, a radiator ineluding a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency, from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, and means for selectively energizing said sheet in a plurality of different modes to provide in succession a plurality of highly directive beams of energy, each having their maxima deflected from a line normal to the plane of said sheet, and further means for so coupling a receiver to said radiator that the maximum response of said system is along a line normal to the plane of said sheet.

14. Inan antenna system, a radiator includinga plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive Walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength,

cans for applying energy from a source of high frequency energy in a push-pull relationship to a pair of opposing edges of said sheet selectively near one and another of the other opposing edges of said sheet, and for selectively applying energy to said first mentioned pair of opposing edges in an unbalanced relationship, whereby there is provided in succession a plurality of highly directive beams of radiant energy of constant polarization but each having its maxima deflected from a line normal to the plane of said sheet.

15. In a radiant energy system, a radiator ineluding a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating. Wavelength, means for applying energy from a source of high frequency energy in a push-pull relationship to a pair of opposing edges of saic sheet selectively near one and another of the other opposing edges of said sheet, and for selectively applying energy to said first mentioned pair of opposing edges in an unbalanced relationship, whereby there is provided'in succession a plurality of highly directive beams of radiant energy of constant: polarization but each having its maxima deflected from a line normal to the plane of said sheet, and means, for coupling in a pushpull relationship a receiver of high requency energy to said first pair of opposing edges at, substantially their midpoints whereby said receiver has a maximum response to energy arriving along a line normal to the plane of said sheet.

16. In a radiant energy system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, means for applying energy from a source of high frequency energy in a push-pull relationship to a pair of opposing edges of said sheet selectively near one and another of the other opposing edges of said sheet, and for selectively applying energy to said first mentioned pair of opposing edges in an unbalanced relationship, whereby there is provided in succession a plurality or" highly directive beams of radiant energy of constant polarization but each having its marzima deflected from a line normal to the plane of said sheet, and means for coupling in a push-pull relationship a receiver of high irequency energy to said first pair of opposing edges at substantially their midpo-ints whereby said receiver has a maximum response to energy arriving along a line normal to the plane of said sheet, there being further means associated with said last mentioned means for preventing energy from said source from affecting said receiver, said further means including trap circuits effective only for energy levels above a predetermined maximum.

17. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a plurality of coaxial transmission lines each having an inner conductor passing across said channel and connected to substantially the midpoint of one side of said sheet, and an outer shell connected to the outer side of said channel and means for selectively connecting said transmission lines to high frequency transducer equipment, said last mentioned means includin a plurality of line sections coupled to said transmission lines and said transducer equipment, and rotary influence means adapted to selectively cause one of said sections to permit the flow of energy between said transducer equipment and its associated transmission line and to simultaneously block the flow of energy between the remainder of said transmission lines and said transducer means.

18. A, radiant energy system including a directive antenna system and means for selectively coupling said antenna system to transducer means in a plurality of modes whereby the zone of maximum response of said system is regu larly deflected in a pattern about a line of normal directivity of said system, said means including a plurality of tuned line sections, each including an outer shell and an inner conductor connected together at one end, said line sections each having a length equal to one quarter of the operating wavelength, means for coupling each of said tuned line sections to said transducer means and to a transmission line afiording one mode of energization of said antenna system,

a rotary disc covering the open ends of said line sections and having an aperture therein adapted to be successively aligned with each of said line sections.

19. A radiant energy system including a directive antenna system and means for selectively coupling said antenna system to transducer means in a plurality of modes whereby the zone of maximum response of said system is regularly deflected in a pattern about a line of normal directivity of said system, said means including a plurality of quarter wave conductors contained within an outer shell, all of said conductors being coupled to said transducer means and each of said conductors being coupled to said antenna system for one mode of energization, a rotary shutter associated with said conductors and having an aperture adapted to be successively aligned with each of said conductors whereby the coupling between only one of said conductors and said antenna system is eilective at any instant.

20. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each coupled to one of said transmission lines at a distance equal to one quarter a of the operating wavelength from their junction with said transducer transmission line and means for selectively causing one of said sections to present a high impedance to energy of the operating frequency at its junction with the antenna transmission line and for causing the remaining sections to present a low impedance to energy of the operating frequency at their junctions with the remaining antenna transmission lines.

21. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each having an outer shell and an inner conductor, said sections having a length equal to one wavelength at the operating frequency and being closed at each end, each of said 2,4se,41a

sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a distance of one quarter wavelength from their junction with said transducer transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radially about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades.

22. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line'sections, each having an outer shell and an inner conductor connected together at each end, said sections having a length equal to one wavelength at the operating frequency, each of said sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a distance of one quarter wavelength from their junction with said transducer transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radially within a cylindrical casing about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades.

23. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each having an outer shell and an inner conductor connected together at each end, said sections having a length equal to one wavelength at the operating frequency, each of said sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a distance of one quarter wavelength from their junction with said transduce transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radially about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades, the radial length of said parallel blades having a length equal to a quarter wavelength and said rotor having an axial extension ofa quarter wavelength.

24. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each having an outer shell and an inner conductor connected together at each end, said sections having a length equal to one wavelength at the operating frequency, each of said sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a distance of one quarter wavelength from their junction with said transducer transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radially within a cylindrical casing about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades, the radial length of said parallel blades having a length equal to a quarter wavelength and said rotor having an axial extension of a quarter wavelength, the junction of said parallel blades and axial extension being electrically freed from its mounting means.

25. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each having an outer shell and an inner conductor connected together at each end, said sections having a length equal to one wavelength at the operating frequency, each of said sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a dis tance of one quarter wavelength from their junction with said transducer transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radially within a cylindrical casing about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades, the radial length of said parallel blades having a length equal to a quarter wavelength and said rotor having an axial extension of a quarter wavelength, the junction of said parallel blades and axial extension being electricall freed from its mounting means by a quarter wave trap.

25. In a lobe switch for a steerable directivity antenna system, a transmission line from transducer equipment to said lobe switch, a plurality of transmission lines between said antenna system and said switch, all of said last mentioned transmission lines being connected to said transducer transmission line, a plurality of resonant line sections, each having an outer shell and an inner conductor connected together at each end,

' said sections having a length equal to one wavelength at the operating frequency, each of said sections having its inner conductor coupled, at a distance equal to one quarter wavelength from one end, to one of said antenna transmission lines at a distance of one quarter wavelength from their junction with said transducer transmission line, quarter wave blades connected to the inner conductors of each of said sections at a distance of one quarter wavelength from their other ends, said blades being arranged radiallywithin a cylindrical casing about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades, the radial length of said parallel blades having a length equal to a quarter wavelength and said rotor having an axial extension of a quarter wavelength, the junction of said parallel blades and axial extension being electrically freed from its mounting means by a quarter wave trap, said parallel blades and said radially arranged blades being provided with cooperating sparking points whereby spurious sparking is avoided.

27. A lobe switch, as set forth in claim 20, in which. said transmission lines are coaxial lines,

each having an outer shell and an inner conductor, said antenna lines being connected to the end of the outer shell of said transducer line, said outer shell being surrounded by a casing connected to said shell a distance equal to a quarter wavelength from said end and the inner conductor of said transducer line extending beyond said end into said casing a quarter wavelength.

28. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, and means coupled to an edge of said sheet for energizing said sheet.

29. In an antenna system, a radiator including a plane conductive sheet having dimensions of the order of a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being of the order of one quarter of the operating wavelength, a transmission line having a conductor passing across said channel and connected to said sheet at a. point on said periphery, and another conductor connected to the outer side of said channel.

30. In an antenna system, a radiator including a plane conductive sheet having transverse dimensions substantially equal to a half wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure along its entire periphery by a channel having conductive walls and passing around said periphery, the depth of said channel being equal to an odd multiple including unity of one quarter of the operating wavelength, and means coupled to an edge of said sheet for energizing said sheet.

31. In a lobe switch for a steerable directivity antenna system, a coaxial transmission line from transducer equipment to said lobe switch, a plurality of coaxial transmission lines between said antenna system and said switch, all of said coaxial transmission lines comprising an outer shell and an inner conductor, the inner conductors of all of said antenna transmission lines being connected to the end of the outer shell of said transducer transmission line, a casing surrounding the outer shell of said transducer transiission line and connected thereto at a distance a quarter wavelength from the end thereof, the outer shells of said antenna transmission lines being connected to said casing, the inner conductor of said transducer transmission line extending beyond the end of the shell thereof and into said casing for a distance of a quarter wavelength, a plurality of resonant line sections, each having an outer shell and an inner conductor, said sections having a length equal to one wavelength at the operating frequency and being closed at each end, each of said sections having its inner conductor coupled at a distance equal to one-quarter wavelength from theend to the inner conductor of one of said antenna transmission lines at a distance of one-quarter wavelength from the junction with said transducer transmission line, quarter Wave blades connected to the inner conductors of each of said sections at a distance of one-quarter wave-length from their own ends, said blades being arranged radially about a common center, a rotor arranged to rotate about said center, said rotor including a pair of parallel blades adapted to selectively cover said radially arranged blades.

32. In an antenna system, a radiator including a plane conductive sheet having transverse dimensions substantially equal to half a wavelength at the operating frequency, said sheet being isolated at the operating frequency from surrounding structure by means arranged about the entire periphery of said sheet, said means comprising a channel member having a depth substantially equal to an odd multiple of a quarter Wavelength at the operating frequency, and means for energizing said sheet coupled to at least one point on the periphery thereof.

NILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,807,386 Clarke May 26, 1931 1,960,006 Hagen May 22, 1934 2,189,549 Hershberger Feb. 6, 1940 2,228,692 Davies Jan. 14, 1941 2,232,592 Davies Feb. 18, 1941 2,401,344 Espley June 4, 1946 2,404,832 Espley July 30, 1946 2,410,597 Brown et a1 Nov. 5, 1946 2,411,034 Gluyas et a1 Nov. 12, 1946 2,412,159 Leeds Dec. 3, 1946 2,412,160 Longfellow Dec. 3, 1946 2,412,161 Patterson Dec. 3, 1946 2,414,266. Lindenblad Jan. 14, 1947 FOREIGN PATENTS Number Country Date 493,695 Great Britain Oct. 13, 1938 

